The
normal height to which plants grow is a critical trait. In the wild Arabidopsis
thaliana uses the same genetic changes in the biosynthesis of the growth factor
gibberellin to cut its size in half as found in semi-dwarf varieties of rice
and barley that have been bred by people. When expressing the same phenotype,
various plant species apparently fall back on the same genes in their genotype.
There must therefore be so-called "hot spots" whose repeated mutation
produces the same traits that are beneficial in some conditions.

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Long-stem plants may well be a
splendorous in flowerbeds. However, long stalks in a grain field present a
danger to the yield. Tall rice or barley varieties buckle over too easily under
the load of their heavy panicles or ears. During the green revolution in the
1960s, numerous high-yield varieties with half the normal height were produced
for agriculture in developing countries. Many of the rice and barley varieties
owe their short stature to a gibberellin deficiency. Besides linear growth,
this plant growth factor promotes seed germination and the development of the
blossoms. The genetic changes in the semi-dwarf rice and barley varieties of
the green revolution prevent a final step in the biosynthesis of gibberellin. The
mutated gene carries the cryptic name GA20ox1.

Maarten Koornneef and his
colleagues from the Max Planck Institute for Plant Breeding Research in Cologne
have now examined whether Arabidopsis plants in the wild that grow to
only half the height as other members of their same species also have a mutated
GA20ox1 allele as the short rice and barley varieties of the green revolution
do. "We would like to know whether the same genetic causes are found for the
same phenotype through natural selection in the wild as are found through the
artificial selection of plant breeding", explains Koornneef.

Arabidopsis only occurs in the northern hemisphere. The researchers in
Cologne together with their colleagues in other countries have found samples of
semi-dwarf Arabidopsis in 23 locations throughout Europe, Asia, and
Japan. Using genetic crossbreeding experiments, they have shown that this
characteristic can be traced back to a change in the GA20ox1 gene in most of
the plant specimens gathered. This gene is especially interesting in Arabidopsis,
as mutations only cause the semi-dwarfism and have no further negative effects
on the performance of the plants, even though gibberellin is an important plant
growth factor.